Download CH 9 Smooth Muscle Tissue

CH 9
Smooth Muscle Tissue
J.F. Thompson, Ph.D.
Smooth Muscle Cells
• nonstriated = smooth
• uninucleate
Smooth Muscle Tissue
• Lacks the dense fibrous
connective tissue sheaths of
skeletal muscles, but have
delicate endomysium
• Found in the walls of hollow
internal organs (except the
heart)
• Often organized into two
antagonistic layers
(longitudinal and circular)
oriented perpendicular to
each other
Characteristics of Smooth Muscle
• Found in the walls of
hollow internal structures
(digestive, respiratory,
reproductive tracts, blood
vessels)
• Arrector pili, pupil of the
eye, etc.
• Involuntary (unconscious)
• Long, slow contractions,
non-fatigable
Smooth Muscle Tissue
Smooth Muscle Tissue
• May be autorhythmic
• May have gap junctions
• Dense bodies are cytoskeletal
anchors
• Myosin and Actin
myofilaments are responsible
for contraction
Smooth Muscle Tissue
• When the longitudinal
layer contracts, the
organ dilates and
shortens
• When the circular
layer contracts, the
organ constricts and
elongates
Contractions of Smooth Muscle
• Peristalsis – alternating contractions and
relaxations of smooth muscles that squeeze
substances through the lumen of hollow organs
• Segmentation – contractions and relaxations of
smooth muscles that mix substances in the lumen
of hollow organs
Contractions of Smooth Muscle
• Some smooth muscle cells:
– Act as pacemakers and set the contractile pace for whole sheets of
muscle
– Are self-excitatory and contract without external stimuli
• Whole sheets of smooth muscle exhibit slow, synchronized
contractions
– They contract in unison, reflecting their electrical coupling with
gap junctions
Regulation of Smooth Muscle
• Contracts under the
influence of:
– Autonomic
Nervous System
– Hormones
– Local regulatory
factors
End CH 9
Smooth Muscle Tissue